Mikel Duke’s research while affiliated with Victoria University Sydney and other places

Landfill disposals of food result in fugitive emissions of methane—a powerful greenhouse gas (GHG). This desktop study focuses on the cost and GHG emissions associated with food waste diversion from landfills using aerobic digesters with liquid outputs (ADLO). Despite the emerging popularity of ADLO units for food waste disposal, their cost and the GHG emissions associated with their use have not been independently quantified and compared to those of other food waste management options. This study compared landfill disposals, the currently available composting services, electric food dehydrators, and in-sink waste disposal units (garbage grinders). For a food waste production rate of 30 kg d−1, the landfill base case showed the lowest cost at USD 23 week−1. The modeled ADLO cost ranged from USD 20–42 week−1, depending on performance. Dehydrator costs were high at USD 29 week−1, largely due to the high energy intensity of the process. The cost of the current centralized composting was USD 51 week−1. The ADLO option with good performance was estimated to produce 5% of the GHG emissions of a landfill. This study showed that well-performing ADLO technology can be economically competitive with landfills and centralized composting and can markedly reduce GHG emissions.

Lead detection for biological environments, aqueous resources, and medicinal compounds, rely mainly on either utilizing bulky lab equipment such as ICP-OES or ready-made sensors, which are based on colorimetry with some limitations including selectivity and low interference. Remote, rapid and efficient detection of heavy metals in aqueous solutions at ppm and sub-ppm levels have faced significant challenges that requires novel compounds with such ability. Here, a UiO-66(Zr) metal-organic framework (MOF) functionalized with SO3H group (SO3H-UiO-66(Zr)) is deposited on the end-face of an optical fiber to detect lead cations (Pb2+) in water at 25.2, 43.5 and 64.0 ppm levels. The SO3H-UiO-66(Zr) system provides a Fabry–Perot sensor by which the lead ions are detected rapidly (milliseconds) at 25.2 ppm aqueous solution reflecting in the wavelength shifts in interference spectrum. The proposed removal mechanism is based on the adsorption of [Pb(OH2)6]2+ in water on SO3H-UiO-66(Zr) due to a strong affinity between functionalized MOF and lead. This is the first work that advances a multi-purpose optical fiber-coated functional MOF as an on-site remote chemical sensor for rapid detection of lead cations at extremely low concentrations in an aqueous system.

Rational design of high-performance defect-free polyamide (PA) layer on robust ceramic substrate is challenging for forward osmosis (FO) water treatment applications. In this study, we first demonstrated a robust ceramic-based thin-film composite (TFC) FO membrane by engineering a novel nano-composite interlayer of titanium dioxide and carbon-nanotube (TiO2/CNT). The structural morphologies and properties were systematically characterized for different substrates (without interlayer, with TiO2 interlayer, or with TiO2/CNT interlayer) and the corresponding ceramic-based TFC-FO membranes. Introduction of low roughness nano-composite interlayers with decreased pore size created an interface with improved surface characteristics, favoring the formation of a defect-free nano-voids-containing PA layer with high cross-linking degree. The resulting ceramic-based FO membrane had a water permeability of approximately 2 L/(m2 h bar) and a NaCl rejection of 98%, showing simultaneous enhancements in both compared to the control membrane without interlayer. Mechanism analysis indicates that such a special nano-composite interlayer not only provided more active cites for the formation of thinner defect-free nano-voids-containing PA layer without penetration into substrate, but acted as a highly porous three dimension network structure for rapid water transport. This work provides a novel protocol for rational design and fabrication of high performance multi-layered inorganic FO membrane as well as extended applications in water treatment with enhanced performance.

This work shows for the first time the convenient in-situ UV illumination of a titanium dioxide (TiO2) photocatalytic membrane via a porous glass substrate for effective fouling reduction during water treatment. By directing light through the light conducting substrate, this concept overcomes the current challenge of photocatalytic membranes that direct light through turbid, light obstructing feed waters. The effect was demonstrated on an immobilised TiO2 membrane fabricated on sintered porous glass. Fouling was tested by filtering model solutions of humic acid (HA), bovine serum albumin (BSA) or sodium alginate (SA). Photocatalysis initiated by simply directing light via the permeate side through the porous glass substrate led to significant reductions in trans-membrane pressure (TMP) rise rates between backwashes and all model organic fouling compounds. Specifically, the UV-light exposed membranes showed a 3.0-fold and 2.4-fold reduction in total filtration resistance for BSA and SA solutions, respectively, which also showed 2.7-fold and 4.2-fold reductions in the irreversible fouling indices. Analysis by SEM coupled with fouling modelling showed the beneficial photocatalytic effects stemmed from reduced intrusion of organic material inside the TiO2 membrane pores, as well as reduced cake layer resistance. The novel, convenient light conducting photocatalytic membranes concept could be used for sustainable, low-chemical membrane filtration of polluted water.

Desalination and water reuse are important means to resolve local water scarcity and security issues worldwide where membrane distillation (MD) may be part of a solution. Natural organic matter and in particular, humic acids (HA), are widely present in water supplies to be treated but exhibit little understood behavior to diffuse through MD membranes into permeate. In this work, air gap (AGMD) and water gap (WGMD) were utilized to study HA behavior in MD using seawater and synthetic water over a range of typical MD temperatures, flow rates and membrane types. HA diffusion was first shown with seawater feed then on synthetic solutions at all process conditions. While electrical conductivity rejection was always above than 99%, HA rejection showed values of 33% and 90% for AGMD and 68% and 93% for WGMD with seawater and synthetic water, respectively. Analytical techniques were used to perform a preliminary organic matter characterization in permeate, obtaining clear differences between the feed and permeate HA property. Compared to hydrophobic membranes, uniquely oleophobic membranes inhibit HA diffusion suggesting hydrophobic surface diffusion of HA through the membrane. HA flux as well as potential undesirable effects of the organic matter in permeate should be considered for MD applications.

The photocatalytic degradation of humic acid (HA) in aqueous suspension using commercial TiO2 powder (Degussa P 25) irradiated with UV light was investigated. Photocatalytic experiments were carried out as an individual treatment and combined with ceramic membrane filtration. In this study, the photocatalytic oxidation of HA was investigated and compared at different operating conditions. The effects of operating parameters such as TiO2 concentrations, HA concentrations, and UV intensity were evaluated on the performance of photocatalytic oxidation process. The effect of salinity on the performance of combined photocatalysis and ceramic microfiltration (MF) system was investigated. The interaction between the components in the system, HA, NaCl, and TiO2 photocatalyst, played an important role in the observed flux change during ceramic MF. The result showed that TiO2 concentrations of 0.5 g/L resulted in significant HA removals of more than 80% after 120 min of photocatalytic oxidation process alone. The result shows that the flux decline was lower in the presence of NaCl compared to absence of NaCl. The observed permeate flux decline behavior during ceramic MF was associated with the composition of HA, and NaCl and TiO2 concentrations after photocatalytic treatment. The results for this hybrid system showed that the DOC removal was 48% in the absence of NaCl and 51 and 55% for 500 and 1000 mg/L NaCl concentrations, respectively after 75 min (15 min dark and 60 min photocatalytic reaction) of photocatalysis and 30 min of ceramic MF. On the other hand, the reduction in UV absorbance with and without NaCl concentrations was more than 75% for this hybrid system.